This invention relates to a photothermographic silver halide imaging element containing a blocked inhibitor which is an amido compound, as a contrast enhancer precursor. It further relates to methods of image formation utilizing said element.
In photothermographic film systems used to capture full color images, once the film has been developed the scanning of the scene luminance content is only possible over a limited density range, determined by the scanner design. If the film densities are too high, scanning is either not possible or becomes subject to signal to noise problems and scene information is lost. It is essential to design color photothermographic films to have sufficient latitude; that is, to be capable of recording all required scene luminance information in a density range that can be scanned. Therefore, such film designs must have a lower gamma and so reach a lower maximum density in each color record than is normal for conventional films.
It is well known that certain heterocyclic molecules with relatively acidic hydrogen atoms bonded to a ring nitrogen or an adjacent sulfur atom act as development restrainers or inhibitors in photographic film and paper systems. Development inhibitors are utilized to either slow or stop development of silver halide grains. They can be used to correct unwanted dye absorption, improve sharpness and reduce granularity of films. Various methods have been described for chemically blocking these inhibitors, so that they can be stable to storage in the film but can be released in a timely fashion upon development. Release of inhibitor typically is achieved under aqueous alkaline conditions by reaction with base or other nucleophile in the processing solution. In particular, blocked inhibitors have found use in image transfer systems. Research Disclosure article 13118, March 1975 and U.S. Pat. Nos. 4,255,510 and 4,256,881 describe materials that use alkali-hydrolyzable groups to block the inhibitors, specifically N-mono substituted and N, N-disubstituted amido groups. Other methods of non-imagewise release involving reaction of a suitably blocked inhibitor with base or other nucleophile in the processing solution, such as described in U.S. Pat. No. 5,354,650, are known but have not been found useful in photothermography.
In conventional photographic systems, such as color negative films, the addition of free inhibitors, even in small quantities, leads to loss of sensitivity. It is therefore useful to release inhibitors imagewise by chromogenic development using, for example, Development Inhibitor Releasing (DIR) couplers. DIR couplers are used to control film response to light by reducing photographic gamma in an imagewise fashion. However, in many cases DIR couplers are not effective gamma reducers in photothermographic systems.
It continues to be a problem in photothermographic films to provide materials that control photographic gamma and enable wide latitude without a significant loss of sensitivity.
This invention provides a silver halide photothermographic imaging element comprising at least one silver halide emulsion layer, said silver halide element further comprising an amido compound of Formula I 
wherein INH is a development inhibitor;
LINK is a linking or timing group and m is 0, 1 or 2; and
R1 and R2 independently are a hydrogen atom or an aliphatic, aromatic or heterocyclic group, or R1 and R2 together with the nitrogen to which they are attached represent the atoms necessary to form a 5 or 6 membered ring or multiple ring system, or R1 and R2 are independently a xe2x80x94C(xe2x95x90O)(LINK)m-INH group, or are substituted with a xe2x80x94NR3C(xe2x95x90O)-(LINK)m-INH, with R3 being defined the same as R1 or R2, with the proviso that only one of R1 and R2 can be a hydrogen atom.
This invention also provides a method of image formation comprising the step of scanning an imagewise exposed and developed imaging element containing an amido compound to form a first electronic image representation of said imagewise exposure. It further provides a method of image formation comprising the step of modifying said first electronic image representation to form a second electronic image representation and a method of image formation comprising storing, transmitting, printing, or displaying said electronic image representations.
This invention also provides a method of image formation comprising the use of an imaging element containing an amido compound in a one-time-use camera and a method of image formation comprising the step of thermally processing an imagewise exposed element formulated as above in a one-time-use camera having a heater stage.
The amido compounds utilized in the invention provide photothermographic silver halide elements, which have low photographic gamma and long latitude. The amido compounds also provide for balanced responses of the different color records thereby giving similar latitudes for the records. This can lead to simpler, less expensive and potentially more robust film scanner designs, which can enhance dispersed photofinishing options. The amido compounds further provide for enhanced shelf life of the photothermographic film and improved response to temperature variations of thermal processing